For the purpose of saving power, illuminating devices usually utilize LEDs (light-emitting diodes) as a light module. However, for emitting white light from the light module, a fluorescent layer is coated on a blue LED to transform a part of blue light to yellow light, and then the blue light and the yellow light are mixed to form white light. After the blue light, which has a higher circadian stimulus, is emitted to the retinas of users, melatonin may be inhibited by the biological clock system, and work efficiency may be increased. However, the blue light emitted by a conventional blue LED has a wave peak in a range from 445 nm to 460 nm. According the luminous radiance biological safety standards, IEC 62471, the blue light having the wave peak has the most hazardous to the retinas of people's eyes.